Separation of fatty oil substances



Sept. 13, 1960 T. H. MCGUINE ETAL 2,952,596

SEPARATION OF FATTY OIL SUBSTANCES Filed April 2, 1959 4/ 71006 v High 6. 7720x 4 ad/ 71," fownult /f United States PatentO SEPARATION OF FATTY 01L SUBSTANCES Thomas H. McGuine, Glenside, Pa., and Walter E. Moss,

Redondo Beach, Calif., assignors to Wilson & Co., Inc., a corporation of Delaware Filed Apr. 2, 1959, Ser. No. 803,733 9 Claims. (Cl. 260-419 This invention relates to the treatment of fatty materials. More particularly, it relates to separation of fatty materials such as fats, fatty oils and fatty acids derived from vegetable, land, marine, animal or other sources to produce purified fractions thereof. Still more particularly, it relates to a method of separation of saturated fatty acids in crystalline form from solvent solutions of mixtures of saturated and unsaturated fatty acids and apparatus for carrying out said process.

It has been common practice to separate the fatty acids of lard or tallow into commercial stearic acid and red oil by a pressing operation. In such a procms, the mixture offatty acids, for example, obtained from tallow and containing approximately 50% of saturated fatty acids generally in the ratio of about 30% palmitic acid and 20% stearic acid, together with unsaturated fatty acids usually of the order of 45% oleic acid is subjected to successive pressing operations. room temperature or below and at these temperatures the palmitic and stearic acids are solids. The pressed solids are known as commercial stearic acid The liquid which is removed by the pressing contains the oleic acid The mixture is pressed at i 1 and is known as red oil. This pressing operation is slow and gives poor recovery of saturated fatty acids. To improve quality, the solids are given a second pressing at higher temperatures to remove more of the liquid fatty acid and produce a material known as double or triple pressed stearic acid.

Separation of mixed higher fatty acids into solid and liquid components has also been effected by the use of solvents. In these processes where the fatty acid mixture and solvent are either independently prechilled or the solvent-fatty acid mixture composition is rapidly chilled, the fatty acids crystallized from solution are particles of relatively small fine size. The physical character of the crystals is such as to present a filtering problem becausethe fine fatty acid crystals enmesh appreciable quantities of red oil making separation of a low iodine number stearic acid a problem. Further, the small particle size crystals present separation problems because, for example, in vacuum filters the operations are subject to cloth blinding, vacuum maintenance, wash nozzle clogging, imperfect spray patterns and other mechanical difiiculties.

In accordance with the present invention, a crystalline fatty material is produced having a particle size large enough to be separable by ordinary screening methods if desired. In this process, a mixture of fatty materials, one

component of which will form supersaturated solutions under the refrigeration conditions to be maintained, is dissolved in a suitable solvent. A relatively large, substantially constant volume of solvent solution of fatty material is established in a liquid flow zone seeded with a multiplicity of crystals of crystallizable component havculation liquid from the flow course is admixed with fresh feed and the admixture passed through .the' external cir- .g.;

2,952,696 Patented Sept. 13, 1960 cuit which circuit includes a heat exchange zone. Cooled solvent solution is delivered to the contact portion of the liquid flow zone, i.e., that portion of the liquid flow zone having the heaviest concentration of the largest size crystals. Admixture passed through the heat exchange zone is cooled to the metastable supersaturated stage. Introduction of the supersaturated solution into the contact portion of the liquid flow zone continuously, maintains an area of supersaturated solution-suspension in which the crystal nuclei grow. Solution displaced from this area and depleted of its supersaturation is removed from the liquid flow zone. A portion of this removed liquor is used for recirculation and the remainder of the liquor removed is one. of the products of process. Crystals of fatty material are withdrawn continuously or periodically from the contact portion of the liquid flow zone and any solution withdrawn with the crystals is separated therefrom and returned to the system.

In a preferred form of the process, a mixture of normally solid and normally liquid fatty acids such as tallow fatty acids are dissolved in a solvent such as acetone, An appreciable volume of this solvent solution is accumulated in a vertical liquid flow zone provided with anappreciable volume of said crystal nuclei of varying sizes. An appreciable minor portion of the liquid in the liquid flow zone, of the order of to A of the volume of said liquid flow zone or greater is withdrawn per minute, is mixed with fresh feed solution, and the mixture is passed through an external heat exchanger. ,Solution cooled to the metastable supersaturated state, i.e., to. a temperature in the range of 5 C. to about -20 C. is introduced into the contact portion of the liquid flow zone. supersaturated solution is quickly depleted of its supersaturation predominantly by deposition of fatty acids on crystal nuclei. With good operating technique new crystal initiation can be held to a rate providing just about the newly required nuclei for a continuous self supporting system. When some unbalance occurs causing an excess of small crystals, a side stream suspension of fine crystals may be withdrawn, the suspension warmed until a homogeneous liquid is obtained and the homogeneous solution returned to the system. Saturated fatty acid solution flows upward through the liquid flow zone and is withdrawn from the top or a point adjacent the top of the liquid flow zone. Liquid is removed from the liquid flow zone for recirculation at a point intermediate the top outlet-and the supersaturated solution inlet. This liquid withdrawal should be at a level providing for a minimum entrainment of fine crystals, i.e., 10% by volume of the drawofi maximum and preferably 4 to 5%. e In this system, crystals of fatty acid grow untilthe crystals no longer are maintained in. suspension at the flow rate prevailing or to the desired particle size, which may be a suspendable size. Large crystals accumulated in the very bottom of the holding zone, may be grown until the crystals withdrawn are 100% retained on a. mesh or mesh or othe desirable standard screen. -A typical product had the following particle size analyses.

'- Cumulative Mesh size: percent retained 10 5.5

Solid fatty acid crystals or particles of such size may be separated from mother liquor withdrawn from the :contact zone with the solids, by decantatiomscreening,

filtration or "centrifugation.

Apparatus for carrying out this process comprises a liquid holder providing a fluid flow course of appreciable volume. Within this liquid flow course there is maintained seed crystal material of varying sizes and a liquid flow rate such'that small crystalline solids norrnally do not leavefthe; equipment with the solvent solution o 7 liquid material. -When a circulation liquid is withdrawn materials. At a concentration of tallow fatty acids in the solution delivered to the inlet to the crystallizer in the range between 0.1% and 0.5% by weight, satisfactory production of crystals occurs at temperatures between about 10 C. and about -20 C. For cottonseed oil fatty acids treatment, satisfactory crystallization occurs in the temperature range between 5 C. and C. when circulating solutions containing 0.17% and 0.5% of cottonseed fatty acids.

Crystallizable 'fatty acid-bearing materials tend to crystallize from solution quickly upon attaining a slight degree of supersaturation. Having a low tolerance for supersaturation, the solutions of fatty acid-bearing materials rapidly attain the labile stage of spontaneous crystal- A crystalline product zone may also be'created by suitable partitioning means such as screens of a mesh size which will pass growing and settling small crystals but preventing passage of selected sized particles out of thecontact zone other than through product removal channels. r

. The contact portion of the liquid flow course is'proyided with a slurry conduit and control means for with: drawing mother liquor and crystals or solidified particles of-fatty materials to a surge tank. This surge tank will act as the feed tank for suitable liquid-solids separation apparatus. 7

Depending upon the mode of operation, it maybe des'i'rable to provide suitable drawofi conduit and control means for that intermediate portionof the liquid flow zone where small size particles are accumulated. Slurry withdrawn at this stage of the crystallizing operation jean be warmed to produce a homogeneous solution which can be returned to the system or otherwise treated to remove fine crystals. 7 Associated with this liquid flow zone is a heat exchanger. The flow zone and heat exchanger are provided with conduit for series flow of solution, out flow from the liquid flow zone being at a point intermediate the; contact portion of the zone and the liquid product drawoif and the liquor delivered from the heat exchanger being introduced into the liquid, flow zone at a point insuring contact and mixing initially with the slur y of the largestparticles of crystal nuclei in the systcm. There is also associated with the two above mentioned members of the system a feed tank for fatty material adapted 'with suitable heating equipment, a feed tank for solvent adapted 'to deliver a cold solvent and suitableinixing means capable of providing intimate and usually turbulentmixing. Fatty materials are poor heat) transfer media. In the heat exchanger, crystallization, to be economically feasible, must be at as fast a rate as is possible and at the same time compatible with control. The driving force for the crystallization operation is the extent of the supersaturation created without spontaneous crystallization. This driving force is usually measured in terms of the number of degrees centigrade below the saturation tem- 'perature of the solution which can be maintained. while holding the supersaturated crystallizable component in solution, assuming of course, the presence of only a minimum of nuclei for initiating crystallization or the failure to attain the labile stage of spontaneous crystallizationWThis driving-force, for 'red oilsolvent solu- Iti'ons of tallow fatty acids is of the orderof' it) to 14 C.

Concentration of'the fatty; material in thesolvent solution materially alters the temperature at which crystallization-from solvent" solution will occur. 'Too' high a -concentration of fatty materials produces solutions which become. too viscous and have characteristics, which interfere; with the crystallization of the fatty material in the .glcsiredphysical form. The concentration best suited for crystalhzatmn will vary for the various different fatty lization which accounts for the production of myriads of small particle size crystals.

Attempts to product fatty acid-bearing crystal material of a particle size greater than 100 mesh i. e., retainable on an 80 mesh U.S., standard screen, from solutions such as are used for cold filtration operation whether of the solvent-aided type or no,t,,in the commercially available crystallizers usedin the, sugar andsalt industries, for example, in equipment such as the Krystal Krystallizer sold by. the Struthers-Wells Company, have failed;

' solution being cooled, i.,e., passedsthrough the heat ex changer. V 1 It has now been discovered that finescrystal formation can be minimized and .controlled and a solvent solution of. the fatty acid-bearing material may be desensitized to the solution shocking efiects of cooling at the necessary high heat transfer rates so. as to prevent premature crystallization and permit release later of the supersaturation of they solution at a point removed from the heat exchanger zone. 1 V

- Successful operation ofa process for crystallizing, for example, normally solid fatty acids from mixtures. of normally solid and normally liquid fatty acids, commercially feasible quantities of crystals substantially all of which are retained on an 80 mesh screen is attained through a combination of mechanical operations and control over the composition and physical nature of the solvent solution of fatty acids being circulated and cooled. By commercially feasible quantities is meant those wherein crystals are produced in, amounts exceeding about 1400 lbs. perrhour utilizing a crystallization 'zone have a capacity of about 5.0 gallons of solvent solution of ,fatty acids and. an" input of. fatty acid mixtures, of, for example, tallow acids of 25.00 lbs. per hour. I g In accordance with the preferred form of carrying out the present invention, a mixture of separable normally liquid and normally' solid fatty acidsis dissolved in a suitable solvent. This solvent solution is cooled-to a temperature at which the solution is saturated, Such a solution is introduced into: a system consisting of a; heat exchange zone and a holding zone. jointed togetherjin a continuous circuit with means for circulation of an appreciable portion. of the volume of the holding tank throughthe heat exchanger; for; example, passage ofrthic cntire liquid volume of the holding tank, through. the heat of' between about -5 and about .10

cula'ting. liquid: are less'active. as initiators of crystallizabroadened. .and crystallizing makes possible an efficient crystallization operation.

t ion than fine fragments produced by the shattering 'of these old crystals and therefore can be tolerated in greater quantity than so-called fines. Accordingly, the conditions of liquid flow for recirculation liquid between the flow course and heat exchanger become of primary importance. In particular, turbulent conditions which could result in any appreciable shattering of fatty acid crystals carried in the recirculation liquid are to be avoided. If pumps are utilized ahead of the heat exchanger, these pumps should be such as to minimize production of fine crystalline material, for example, an axial flow pump, a pump of reduced pump blade velocity, etc. to be sure that the crystal fines are not built up-due to crystal shattering.

When the content of old crystals in the recirculating liquid is maintained below by volume and preferably below 5% by volume and the suspension is not subjected to violent agitation, the supersaturated solution shows a minimized tendency toward premature deposition and the solution passes through the heat exchanger leaving it in a clean condition with the surfaces thereof substantially free of solids and thus in a position to maintain the necessary heat transfer rate.

In addition to the solids content of this recirculated liquor, the solution portion thereof must be maintained in the metastable as distinguished from labile state while passing through the heat exchanger. Maintaining the solution composition in a state where the supersaturated solution is still in the metastable condition after cooling we have found, may be attained by the addition of desensitizing agents. For example, if in a crystallizing operation the suspension issuing from the heat exchanger has been lowered in temperature to -12 C., the solution must have a composition which remains in the metastable state at this temperature. For example, the solution phase must not attain the labile state until the solution is at least 2-5 below this 12 C. temperature. Sensitivity of the fatty acid solution is illustrated by failure of the process to be operative when using a refined oil such as white oil, a product which has miscellaneous materials removed therefrom such as glycerides, phosphatides, polymers, color bodies, etc.

The exact nature or chemical composition of the desensitizer for fatty material-solvent solutions is not known. It is known that unrefined tallow fatty acids contain at least one form of the desensitizer or stabilizer. Fatty materials, for example, saponified tallow acids and the separated red oil therefrom, saponified vegetable oils, etc., still bottoms from distillation of red oil have been found to contain some form of the desensitizer compatible with the fatty materials to be separated.

Mixtures of separable fatty materials which in the normal state have too narrow a temperature range of metastable condition to be separable by the herein described method, may be rendered amenable to such treatment by the addition of stabilizer or desensitizer-containing liquids. For example, if white oil is used as the starting menstruum for filling the crystallizer system which will be fed a solution of tallow fatty acids for separation, lowering the temperature of the white oil below about +3 C. and maintaining a temperature differential between refrigerant and white oil of more than 5 C. results in the precipitation'of fine solids. When about 3% by volume of red oil distillation still bottoms are added to the white oil, the cloud point of the menstruum is lowered to about -8 C. and a temperature differential may be maintained across the heat exchanger wall of 10 to 14 C. without shockingthe solution into crystallization, i.e., the metastable temperature range is Maintenance of this high AT for cooling Fatty acid materials which may be used as feed stocks for this process are the mono or polybasic fatty acids or triglyceride fats. The primary requirement is that the materials to be separated have a sufiicient solubility dif ference at some specific temperature, in a desired solvent. Separations can, for example, be made between red oil and stearic acid found in tallow and grease. Cottonseed soap stock can be separated into cottonseed stearine acids and a high iodine value drying fatty acid. Polybasic fatty acid mixture separations may be illustrated by the separation of azelaic acid from a mixture of that and pelargonic acid. Other illustrative separations which can be effected are lauric acid from coconut fatty acids, ester separation such as methyl laurate from methyl stearate, lard oil from lard, oleo oil from oleostearine, and the like.

In carrying out the process, fatty mixtures at a temperature slightly above the melting point of the highest melting component thereof is premixed with solvent. This solvent is introduced at a temperature and in proportion such that the resultant solvent-fatty acid mixture has a temperature required to give a clear solution.

Solvent useful in this process may be a polar solvent or a nonpolar solvent. 'For example, the lower molecular weight alcohols having 1 to 6 carbon atoms in the hydrocarbon group or groups such as methyl and ethyl alcohol; ketones such as acetone, methyl ethyl ketone and the like; hydrocarbons such as pentane, hexane, benzene, xylene, naphtha and hex-aline; substituted hydrocarbons, such as ni-tromethane, and dioxane, and even unsaturated oils low in saturated acids such as red oil, destearinated soya and cottonseed oils, or compatible mixtures thereof may be used.

The solvent is prechilled to a temperature between about +1 0 C. and about 50 C. depending upon the particular solvent and the solidification temperature of the fatty acid material to be processed. When utilizing the preferred solvent, acetone is cooled to between about l0 C. and about 25 C. If a solvent such as acetone contains water, which tends to sharply decrease the solubility of the solid fatty material or fatty acids, the solvent temperature can be elevated to about +10 C. and the separation of fatty materials and solvent made at a temperature higher than in the absence of water. It must be borne in mind that, when water is used, the ratio of water to solvent must be limited to below the point where phase separation occurs in the cold slurry itself. Water content of the solvent is usually limited to a maximum of about 15% and preferably to about 5% by volume.

It is preferred to use about three parts by weight of solvent to one part by weight of fatty materials, for ex,- ample, mixed fatty acids for the crystallization process. The lower limit of solvent ratio is dictated by the solubility of the oil component at the temperatureof the cooler and the viscosity of the circulating liquor at the crystallizing temperature. The upper limit of solvent ratio is dictated by the economics of solvent recovery and the capacity of the equipment. Moisture or water when used in a solvent such as acetone tends to slow down crystal agglomeration causing difficulty in operating the crystallizer. Water has another bad effect when using saponified fatty acids containing unsplit glycerides in that'it tends to shock these components from solution causing a fines problem in operating the crystallizer. The preferred water content in the case of a solvent such as acetone is about 5%. However, other proportions of solvent to fatty acids varying from about 2:1 to about 5: 1 may be used in the preparation of the solvent solution.

When mixing precooled solvent and fatty materials some cooling is obtained from the acetone. The final cooling is obtained by means of a cooler outside the crystallizer unit. This method of cooling promotes supersaturation of the solution without depositing solids on any cooling surface and eliminates the need for crystallizens with scraper blades such ,as have been utilizedin the fatty acids After passage through the external cooler where. the

7 temperature of the solution mixture is reduced to a temperature in the range between about 40 C. and about +20 C. the solution is passed through the tank holding particles of crystallized sol-ids. The optimum temperature of operation will vary depending upon the solvent, solvent ratio, moisture content of the chilled solution, type of fatty acids and the desired purity of the separated components of the mixture. Using acetone as a solvent containing 0.1% water and a solvent ratio of 3:1, tallow fatty acids for example can be separated at 15 C. to produce a finished red oil of 0.0 C. titer and finished s'tearic acid having an iodine number of 12. It this moisture is increased to 5%, the same end products can be produced while operating at -l C. When a finished red oil having .a titer of about 6 is acceptable, the operating temperature may be raised to C. Using benzene as a solvent, stearyl alcohol can be separated from lauryl alcohol at a temperature of about +l0 C. Using methyl alcohol as the solvent, azel-aic acid can be separated from pelargonic acid at a temperature of about 0 C.

' "The separation of the fatty acid materials is directly related to crystal size and form. While applicants have no intention of being limited by theory, itis believed that crystallization in the instant process is accomplished by maintaining the supersaturation of the solvent solutions primarily in the metastable condition, and broadening the metastable range through the presence of materials inhibiting immediate spontaneous crystallization.

Residual filter cake either before or after it is removed from the filter is washed with solvent cooled to a temperature of for example in the case of tallow acids about -l5 C. to 0 C. It is preferred to maintain a solvent to fatty acid ratio in this washing operation in the order of about 1:1 to about 2:1. The wash solvent is removed from the filter cake by filtration and is preferably recycled back to the makeup solvent feed tank.

Residual solvent is removed from the washed filter cake by evaporation, preferably under vacuum. The resulting washed filter cake from tallow acids is equivalent to commercial grade stearic acid.

Solution of solvent and fatty material, from which the crystallizable fatty solids have been removed, under readily controllable processing conditions, are clear solutions. I-f solids carry over at this point, the solids can be removed bysuitable filtering apparatus. Solvent is removed fromthe clear solution by evaporation, preferably under vacuum. The residue remaining after solvent "evaporation generally constitutes a commercially acceptable product which does not require processing such as purification.

Apparatus adapted to carry out the process of this invention is schematically illustrated in the attached drawing. i In'this drawing, the numeral 10 indicates a feed tank for fatty material, for example, fatty acids, Tank 10 is. provided with a heating element 1-1 such as a steam coil capable of heating or maintaining the fatty acid material at a temperature up to about 130 F. Tank 10 discharges fatty acid material through conduit 12 to suitable mixing equipment 13 provided with cooling means '14. Solvent for the system is supplied from feed tank 15. Solvent is delivered from tank 15' to mixer 13 through pipe 16.

Solvent-fatty acid mixture is delivered from mixer 13 through conduit 17 and joins liquid in pipe 18' for pump- {ing by suitable means 18A to suitable heat exchanger 19.

*Cooled liquid is delivered through conduit 20 to the bottomof a holding tank 21. Tank 21 may be of suitable 'design such as tank units known as Krystal Krystallizers,

, manufactured by Struthers Wells Corporation or equivalent units produced by other companies, for instance ".Swenson Evaporator Company. 7

Tank 21 is provided with crystalline solid fatty acids reed 22. l f 7 8 Tank 21is provided with outlet conduit .23 for slurry of coarse particle size solids, outlet conduit 24 tor fine particle slurry and outlet conduit 25 for solvent .solution relatively free of solids. Each outlet is provided with suitable :flow control means, 26, 2.! and 28, respectively. Conduit .23 delivers coarse particle size slurry to a surge tank 29. Slurry is delivered from tank '29 to a solids. separation apparatus 30 such as a centrifuge through pipe 31, apparatus 30 being indicated for simplicity as having a separation portion 30a. and :a washing portion 30b. pMother liquor returns through pipe 50 and valve 50a to pipe 18. Separated solids are delivered by conveying means 32 such as a belt to drying apparatus. Solvent recovered in drying apparatus 33 is discharged through pipew3'4 under control of valve means 34a to pipe 39. Solid product is discharged by conveying means 35 to storage. h

Solvent solution discharged through outlet pipe 25 is delivered. to suitable'solvent vaporing means 36 such as an evaporator. Vapors from evaporator 36 are de livered through conduit 37 to condenser 38' and cooled by passage in heat exchange relationship to coolant solution. Condensed solvent is delivered from condenser 38 through pipe 39 to the solvent storage tank 40 from whence it is distributed by line 41, under control of valve 41a, to tanks 15 and 42. Tank 42 is provided with a cooling coil 43. Cooled solvent is delivered by pipe 44 as cold wash solvent for the crystal product to solids separation apparatus 30b. Wash solution is delivered to mixer 13 through conduit '34.

Solvent free fatty acid component is delivered to storage from evaporator 36 through pipe 45; Slurry of saturated solvent solution and small particle size crystals are delivered through conduits 24 and 46 to crystal settler-dissolver 47. Slurry is heated to eifect solution of the crystal solids by heating means 48. Solu tion from settler-dissolver 47 is delivered by pipe 49 for mixing with feed flowing in pipe 12.

The invention or its advantages will be more fully understood from the following detailed examples given by way of illustration and without any intention that the invention be limited thereto.

Example I Titer, C 4 1.8 Iodine number 45.3 Acid number 199.3 Saponification number 2035 were converted to a liquid condition by heating 'to a temperature of about 55 C. Acetone solvent was cooled to a temperature of 0 C. One part by weight of the above tallow fatty acids was mixed with 1% parts by weight of cool acetone and the resulting mixture cooled using circulating water of 26 C. to approximately 30 The liquid flow zone or crystallizer was charged with a mixture the components of which had a ratio of 57 lbs. of redoilto lbs. of acetone. The red oil had the following analysis:

Titer, C

Iodine number 83.6 Add number 194.1 -Saponification number 200.3

7 The charge stock in the crystallizer was circulated to a heat exchanger at a rate of 15 gallons per minute out oft-he exchanger. Cooling was applied to the heat exchanger by means of cool circulating brine at a temperature of 13" C. This refrigeration cooled the crystallizer charge stock to 10 C. in 1% hours, at which time '3 lbs. of pulverized crystalline stearic acid was in- 215 troduced into the crystallizer chamber as :seed material.

' 9 At this point, the circulating rate through the heat exchanger was reduced to 5 gallons per minute. Seed crystal material entrained in liquid being circulated was determined to be approximately 1% by volume.

Cooling brine introduced into the heat exchanger was gradually reduced in temperature over a period of 3 hours to approximately -25 C. With a flow rate of 5 gallons per minute a temperature difference of between about 8 C. and about 10 C. was maintained between this cold brine and the circulating liquor. When the circulating liquor reached a temperature of -l5 to 16 C. feeding of the acetone solution was begun, the feed stock being admixed with circulating liquid at a location close to the inlet to the heat exchanger. The feed rate was approximately 4.5 lbs. of acetone-tallow fatty acid solution per hour. The amount of crystalline fines in the circulating liquid gradually rose over a period of 3 hours at which time material was withdrawn to the fine crystal settler-dissolver. This settler-dissolver was held at a temperature of 15 C. to 16 C. by means of a heating element. The amount of slurry passing through the settler was approximately A of the volume of liquid being circulated from the crystallizer to the heat exchanger. Clarified liquor from the settler-dissolver was reintroduced into the feed to the system. After two hours of operating with this side stream removal of fine crystal slurry, the amount of crystal fines circulating through the heat exchanger leveled ofl at about 4% by volume.

Within two hours of starting the acetone-tallow fatty acid feed, the crystallizer has reached an equilibrium point where clear mother liquor consisting of red oil dissolved in acetone could be withdrawn from the liquid flow zone and delivered to the evaporator for recovery of acetone.

After about 14 hours of continuous operation, the crystallizer reached a steady operating state permitting increase of feed rate to approximately 10 lbs. of tallow fatty acid solution per hour while maintaining a circulating liquor temperature of 15 C. to 15.5 C. At this feed rate the temperature difference between the cooling brine and the circulating liquor was between about 11 C. and 14 C. Circulation rate of liquor from the crystallizer to the heat exchanger was maintained at about gallons per minute. With the crystallizer operating at a steady state, a slurry was withdrawn from the bottom of the crystallizer containing approximately 12 to 13% solids by weight. This value was determined by centrifuging a fixed quantity of crystallizer bottom slurry. This slurry was passed to a screening operation to separate crystals retainable on an 80 mesh US. Standard screen. The mother liquor was separated together with undersized particles of crystallizer fatty acids and was returned to the circulating liquor line. Separated solids were washed with acetone cooled to 15 C. This flow of cool acetone was mainmained at approximately 2 to 2.5 times the weight of solids in the separator. This wash liquor was returned to the acetone feed mixer. Washed solids were discharged to a conveyor and transferred to drying apparatus where acetone was vaporized. and thencondensed for introduction back into the system. ,Red oil obtained as an overhead product and stearic acid obtained as a bottom or underflow product had the follow- .ing analyses: a

Example II The identical equipment used for the crystallization of stearic acid in Example I was used for the separation of soya fatty acids. The crystallizer was charged with a mixture having a ratio of 57 lbs. of soya fatty acids having an iodine number of mixed with lbs; of acetone. The soya fatty acids had the following analysis:

Titer, C -'-12.3 Iodine number 150 A feed stock of soya fatty acids was prepared from soya fatty acids having the following'analysis:

Titer, C 26.2 Iodine number 128.3

FINAL OUTPUT Solids Soya Titer, C 50.7 .3 Iodine number 20. 1 145.0 Yield as percent of feed. 13.6 86.4

Example III The equipment, described above and utilized for the operation of the process as described in Example I, was operated using the same tallow fatty acid material as in Example I.

The solvent used diifered from that in Example I in that the acetone contained 5% by weight of water. In the operation the cooling brine to the heat exchanger was reduced only to 20 C. and the liquor circulated between the crystallizer and the heat exchanger was operated at 10 C. instead of -15 C. to l6 C. After reaching the steady state, the circulating liquor was held at a temperature ranging from 7 C. to 10 C. The feed quantity under steady operating conditions was the same as in Example I, i.e., 10 lbs. per hour. The products obtained from this tallow fatty acid feed showed the following analyses:

were converted to a liquid condition by heating to a temperature of about 55 C. n-hexane solvent was cooled to a temperature of 0 C. One volume of the above cottonseed fatty acids was mixed with 1% volumes of cold n-hexane and the resulting mixture cooled using circulating water of 26 C. to approximately 30 C. to serve as feed stock.

The liquid flow zone or crystallizer was charged with a mixture having the ratio of 55 lbs. of destearinated cottonseed acids and 1180; lbs. ofhexane. The destearinated acids had the following analysis:

Titer, C 7.2 Iodine number 127. 1 Acid number 196.3 Saponificationnumber 198.4

The charge stock in the crystallizer was circulated to a heat exchanger at .a rate of 15 gallons per minute out of the exchanger. The cooling was applied to the heat exchanger bymeans of brine andcooled the crystallizer charge stock to -10 C. at which time 3 lbs. of pulverized crystalline cottonseed acids were introduced into the crystallizer as seed material. At this point, the circulating rate through the heat exchanger was reduced to 5 gallons per minute' When the circulating liquor maintained as-an even temperature of approximately C., feed stock was introduced at a location close to the inletto the heat exchanger as described in Example I. The feed rate was approximately 4 /2 lbs. of acetonecottonseed fatty acids solution per hour.

When the crystallizer had reached an equilibrium point in approximately two hours, mother liquor consisting of cottonseed acids dissolved in hexane could be withdrawn from the liquid flow zone and delivered to the evaporator for recovery of n-hexane.

After a period of continuous operation, the crystallizer reached a steady operating state permitting increase of feed rate to approximately 10 lbs. of feed solution per hour. With the crystallizer operating at a steady state, a slurry was withdrawn from the bottom. of the crystallizer containing approximately 10% solids by weight. This slurry was passed to a screening operation. The mother liquor was separated together with undersized particles of solid cottonseed fatty acids and was returned to the circulating liquor line. Separated solids were washed with n-hexane cooled to 10 C. Washed solids were discharged to a conveyor and transferred to drying apparatus where n-hexane was vaporized and then condensedfor reintroduction into the system. Liquid cottonseed acids obtained as an overhead product and solid acid obtained as a bottom orI underflow product had the following analysis:

cottonseed Acids Solid Example V Distilled tallow fatty acids having the following analysis:

Titer, C. Iodine number 55.4 Acid number 7 198.2 Saponification number 198.6

was converted to a liquid condition by heating to a temperature of about 55 C. Acetone solvent was cooled to a temperature of 0 C. 7 One part by Weight of the above tallow fatty acid was mixed with 1. /2 parts by weight of cooled acetone and theresulting mixture cooled using circulating water to approximately 30 C. to serve as feedstock. r 4 The liquid flow zone or crystallizer wascharged with a mixture the components of which had a ratio of 57 lbs.

of white oleine to 185 lbs. of acetone. The white oleine Acid number. 1 202.9 Sapon'ification number 203.0

12 The charge stock in the crystallizer was circulated to a heat exchanger at a rate of 15 gallons per minute out of the exchanger. Cooling was applied to the heat exchanger'by means of cool circulating brine at a temperature "of --l3 C. This refrigeration cooled the crystallizer charge stock to -10 C. in 1 /2 hours, at which time 3 lbs. of crystallized stearic acid was introduced into the crystallizer chamber as seed material.

Cooling brine introduced into the heat exchanger was gradually reduced in temperature to approximately 25 C. When the circulating liquor attained a'temperature difference of the order of 8 to 12 C. above that of the brine the heat exchanger tubes continually blocked up and the process failed to produce large crystals of stearic acid and instead produced large volumes of small crystals. Y

The temperature of the crystallizer solution was allowed to rise to about 0 C. and approximately 2 lbs. of red oil still bottoms were added to the crystallizer and 3% by weight of red oil still bottoms was added to the tallow fatty acid-acetone feed solution. The red oil still bottoms had the following analysis:

Free fatty acids 70.0 Saponification number 180.3 Iodine number 75.0

Cooling was again induced using brine having a temperature of'approximately 25 C. and the circulating liquor reduced in temperature to 15 to l6 ,C. Introduction of acetone feed solution was again started, the feed stock being admixed with circulating liquor at a location close to the inlet of the heat exchanger in identical fashion and the same equipment described for Example I. The feed rate 'was approximately 4 /2 lbs. of acetone-tallow fatty acid solution per hour.

Within 3 hours of starting the acetone-tallow fatty acid feed, the crystallizer had reached an equilibrium Where clear mother liquor consisting of a liquid product identifiable by composition as red oil dissolved in acetone could be withdrawn from the liquid flow zone and delivered to the evaporator for recovery of acetone. After about 14 hours of continuous operation, the crystallizer reached a steady operation state pennitting'increase of feed rate to approximately 10 lbs. of fatty acid solution per hour. At this feed rate, the temperature difference between the cooling brine and the circulating liquor was between about 11 C. and 14 C. As in Example I the circulating rate of liquor from the crystallizer to the heat exchanger was maintained at about 5 'gallons per minute. With the crystallizer operating at a steady state, a slurry of stearic acid crystals was withdrawn from the bottom of the crystallizer and passed to a screening operation to separate crystals retainable on a mesh- US. Standard screen. Separated solids were washed with acetone cooled to l5 C. Red oil obtained as an overhead product and stearic acid obtained as a bottomor underflow product had the following analysis:

Although the invention has been described in connection with specific embodiments thereof, it will be understood that these are not to be regarded as limitations upon the scope of the invention except insofar as included in the accompanying claims.

We claim:-

, 1. The process of producing abnormally large crystals of crystallizable fatty material having a'particle size permitting recovery by ordinary screening methods from an unrefined mixture of crystallizable and non-crystallizable components which comprises dissolving said mixture in a solvent to produce a solution saturated as to the crystallizable component, establishing a relatively large sub 'stantially constant volume of said solution in a liquid flow zone, maintaining an accumulation of varying size crystals of crystallizable component in a contact portion of said liquid flow zone, moving solution continuously through said flow zone, removing solution from said liquid flow zone at a point removed from said initial contact zone, said removed liquid being in an amount constituting an appreciable minor portion of the liquid in said flow course on a per minute basis, admixing fresh feed solution and removed solution and passing said admixture through a heat exchange zone to reduce the temperature of said admixture to a point establishing the solution in the metastable state, delivering metastable supersaturated solution to the contact portion of said liquid flow zone, removing crystallized solids from the contact portion of said liquid flow zone, removing solvent solution substantially depleted as to crystallizable component from a point removed from said contact portion of the liquid flow zone and recovering solvent associated With the removed crystal solids and the non-crystallizable component from the respective products withdrawn from the system.

2. The process of producing crystals of crystallizable fatty material having a particle size greater than 100 mesh fiom unrefined mixtures of normally solid and normally liquid fatty materials which comprises establishing an appreciable volume of solvent solutionrsaturated as to the normally solid fatty materials in a vertical liquid flow zone and an accumulation of varying size crystal nuclei of crystallizable fatty material in the lower contact portion of said vertical flow zone, moving solvent solution constinuously and uwardly through said flow zone, removing solution and associated crystals in amounts constituting an appreciable minor portion of the liquid in the flow zone on a per minute basis from said flow zone ,at a point intermediate the contact portion of said flow zone and the top of said flow zone, moving the removed solution to a heat exchange zone under turbulence conditions avoiding shattering of crystals of normally solid fatty materials and admixing fresh feed solution with said removed solution, reducing the temperature of said admixture to a point establishing the solution in the metastable state in said heat exchange zone, delivering metastable admixture to the bottom of 'said liquid flow zone, removing a slurry of crystallized solids accumulated in the bottom of the liquid flow zone, overflowing a solvent solution substantially depleted as to crystallizable component from a point axially removed from said contact portion of the liquid flow zone and recovering solvent associated with the removed crystal solids and non-crystallizable component from the respective products withdrawn from the system.

3. The process of producing crystals of crystallizable fatty materials having a particle size greater than 100 mesh from mixtures of normally solid and normally liquid fatty materials whose normal solvent solutions rapidly attain the labile state of spontaneous crystallization which comprises establishing an appreciable substantially constant volume of solvent solution saturated as to normally solid fatty material in a vertical liquid flow zone containing an accumulation of varying size crystal nuclei of crystallizable fatty material in the lower portion thereof constituting a contact portion of said flow zone, moving solvent solution continuously and up- 'wardly through said flow zone, removing solution in amounts constituting an appreciable minor portion of the liquid in the flow zone on a per minute basis from said flow zone at a point intermediate the contact portion of said flow zone and the top of said flow zone, passing said removed solution together with fresh solvent feed solution of a mixture of fatty materials through a heat exchange zone to cool the mixture of removed 14 solution and said feed to provide a mestable supersaturated solution, said mixture of removed solution and feed containing a small amount of high boiling component of a fat selected from animal and vegetable fat eifective to stabilize said mixture of removed solution and feed against spontaneous crystallization during cooling to said metastable supersaturated state, delivering metastable solution to the bottom of said liquid flow zone removing a slurry of crystallized solids accumulated in the bottom of the liquid flow zone, overflowing a solvent solution substantially depleted as to crystallizable component from a point above said contact portion of the liquid flow zone and recovering solvent associated with the removed crystal solids and non-crystallizable component from the respective products withdrawn from the system.

4. The process of producing crystals of crystallizable fatty acids having a particle size greater than mesh from mixtures of normally solid and normally liquid fatty acids which comprises establishing an appreciable substantially constant volume of solvent solution saturated as to the normally solid fatty acids of said mixture of fatty acids in a verical liquid flow zone and an accumulation of varying size crystal nuclei in the lower contact portion of said vertical flow zone, moving solvent solution continuously and upwardly through said flow zone, removing solution in amounts constituting an appreciable minor portion of the liquid in the flow zone on a per minute basis from said flow zone at a point intermediate the contact portion of said flow zone and the top of said flow zone, admixing fresh feed solution and removed solution and passing said admixture through a heat exchange zone, reducing the temperature of said admixture to a point establishing the solution in the metastable state, maintaining a concentration up to 3% by weight of fatty acid still bottoms in said solution moving in said liquid flow zone, delivering metastable admixture to the bottom of said liquid flow zone removing a slurry of crystallized solids accumulated in the bottom of the liquidtflow zone, overflowing a solvent solution substantially depleted as to crystallizable component from a point axially removed from said contact portion of the liquid flow zone and recovering solvent associated with the removed crystal solids and non-crystallizable component from the respective products withdrawn from the system.

5. The process of producing abnormally large crystals of crystallizable fatty acid material having a particle size permitting recovery by ordinary screening methods from an unrefined mixture of crystallizable and non-crystallizable components which comprises dissolving said mixture in a solvent to produce a solution saturated as to the crystallizable component, establishing a relatively large substantially constant volume of said solution in a liquid flow zone, maintaining an accumulation of varying size crystals of crystallizable component in a contact portion of said liquid flow zone, moving solution continuously through said flow zone, removing solution from said liquid flow zone at a point removed from said initial contact zone, said removed liquid being in an amount constituting an appreciable minor portion of the liquid in said flow course on a per minute basis, removing a nonhomogeneous second solution portion containing entrained fines from a point intermediate, on a vertical axis basis, the circulating solution takeoff and the liquid product takeoff, rendering the solution homogeneous and returning said homogeneous solution to the crystallizer system containing admixed fresh feed solution and removed solution and passing said admixture through a heat exchange zone to reduce the temperature of said admixture to a point establishing the solution in the metastable state, delivering metastable solution to the contact portion of said liquid flow zone, removing crystallized solids from the contact portion of said liquid flow zone, removing solvent solution substantially depleted as to crystallizable component from a point removed from said contact portion of theliquid tflow-zone and recovering solvent associated with the removed crystal solids and the non-crystalliza'ble component from the respective products withdrawn from the system;

6. The process of producing crystals of product iden- .tifiable as stearic acid from undistilled tallow fatty acid mixtures, said crystals having a particle size permitting recovery by ordinary screening methods which comprises dissolving said tallow fatty acids in a solvent to produce a solution saturated as to the stearic acid establishing a relatively large substantially constant volume of said solution in a liquid flow zone, maintaining .an accumulation of varying size crystals of stearic acid in a contact portion of said liquid flow zone, moving solutioncon- ,tinuously through said flow zone, removing solution from said liquid flow zone at a point removed from said initial contact portion of said flow zone, said removed solution being in an amount constituting at least between about and about of the liquid in said flow course on a per minute basis, admixingfresh feed solution and .removed solution and passing saidadmixture through. a heat exchange zone to reduce the temperature of said admixture to between about 5 C. and about -20 C., removing crystallized solids from the contact portion of said liquid flow zone, removing solvent solution of red .oil from a point removed from said contact portion of the liquid flow zone, recovering red oil from said solvent solution and recovering crystals. of stearic acid retainable ou. an 80 mesh U.S. Standard screen from .the solvent with which they are associated.

7. The process of producing crystals of product idenatifiable as .stearic acid from undistilled tallow fatty acid mixtures, said crystals having a particle size permitting recovery by ordinary screening methods which comprises dissolving said tallow fatty acid mixture in acetone, establishing a relatively large substantially constant volume -.of acetone solution of red oil in a liquid flow zone, maintaining an accumulation of varying size crystals of stearic acid in a contact portion of said liquid flow zone, moving acetone solution through said flow zone continuously, removing acetone solution from said liquid flow zone at a point removed from said initial contact portion of said fflOW zone, said removed solution being in an amount constituting at least between about /5 and about A of the liquid in said flow course on a per minute basis,

admixing fresh acetone solution of tallow fatty acids and removed solution and passing said admixture through a 'heat exchange zone to reduce the temperature of said admixture to between about C. and about C.,

removing crystallized stearic acid from the contact portion of said liquid flow zone, removing solvent solution of red' oil from a point removed from said contact portion of the liquid flow zone, recovering red oil from said solvent solution and recovering crystals of stearic acid retainable on an 80 mesh U.S. Standard screen from the solvent with which they are associated.

16 l 8. The process of producing solid crystal fatty acids from unrefined cottonseed fatty acid mixtures which comprises establishing a relativelylarge substantially constant volume of charge stock comprising about 55 parts of destearinated cottonseed acids and 180 parts of hexane in a vertical liquid flow zone, seeding said charge stock with nuclei crystals of solid acids and maintaining flow conditions such that the larger seed crystals accumulate in a contact portion of said liquid fiow Zone, moving said hexane solution continuously though said flow zone, removing hexane solution from said liquid flow zone at a point removed from said initial contact portion of said vertical flow zone, said removed solution being in an amount constituting at least between about and about 5 of the liquid in said flow course on a per minute basis, admixing fresh feed solution consisting of about approximately 40% cottonseed fatty acids and 60% n-hexane and removed solution and passing said admixture through a heat exchange zone to reduce the temperature of said admixture to between about -2 C. and about 10 C., removing crystallized solid from the contact portion of said liquid flow zone, removing hexane solution of liquid cottonseed acids from a point removed from said contact portion of the vertical liquid flow zone, recovering liquid cottonseed fatty acids from said hexane solution and recovering solid crystals retainable on an 80 mesh U.S. Standard screen from the hexane solvent with which they are associated. V V g 9. In a cyclic process for separating normally liquid fatty materials from normally solid fatty materials from a solvent solution of both which rapidly attains the labile state of spontaneous'crystallization comprising establish ing an appreciable substantially constant volume of s01- vent solution containing said normally liquid fatty materials and saturated with said normally solid fatty materials in a vertical liquid flow zone containing an accumulation of crystal nuclei of said normally solid fatty material in the lower portion thereof constituting a contact portion of said fiow zone, removing supernatant solution from said flow zone above said contact portion thereof,

.cooling said removed solution in the presence of a small amount of high boiling component of a fat selected from animal and vegetable fat to provide a metastable supercooled solution, said added high boiling fat component serving to stabilize the solution which is cooled against spontaneous crystallization during cooling to said metastable supersaturated state and passing said metastable supercooled solution upwardly through said contact portion of said flow zone to cause crystallization of said normally solid fatty materials therefrom.

References Cited in the file of this patent Chem. Engineering, August 11, 1958, pp. 126-l40. Chem. Engineering Progress, May 1959, vol. 55, No. 5, page 47. 

1. THE PROCESS OF PRODUCING ABNORMALLY LARGE CRYSTALS OF CRYSTALLIZABLE FATTY MATERIAL HAVING A PARTICLE SIZE PERMITTING RECOVERY BY ORDINARY SCREENING METHODS FROM AN UNREFINED MIXTURE OF CRYSTALLIZABLE AND NON-CRYSTALLIZABLE COMPONENTS WHICH COMPRISES DISSOLVING SAID MIXTURE IN A SOLVENT TO PRODUCE A SOLUTION SATURATED AS TO THE CRYSTALLIZABLE COMPONENT, ESTABLISHING A RELATIVELY LARGE SUBSTANTIALLY CONSTANT VOLUME OF SAID SOLUTION IN A LIQUID FLOW ZONE, MAINTAINING AN ACCUMULATION OF VARYING SIZE CRYSTALS OF CRYSTALLIZABLE COMPONENT IN A CONTACT PORTION OF SAID LIQUID FLOW ZONE, MOVING SOLUTION CONTINUOUSLY THROUGH SAID FLOW ZONE, REMOVING SOLUTION FROM SAID LIQUID FLOW ZONE AT A POINT REMOVED FROM SAID INITIAL CONTACT ZONE, SAID REMOVED LIQUID BEING IN AN AMOUNT CONSTITUTING AN APPRECIABLE MINOR PORTION OF THE LIQUID IN SAID FLOW COURSE ON A PER MINUTE BASIS, ADMIXING FRESH FEED SOLUTION AND REMOVED SOLUTION AND PASSING SAID ADMIXTURE THROUGH A HEAT EXCHANGE ZONE TO REDUCE THE TEMPERATURE OF SAID ADMIXTURE TO A POINT ESTABLISHING THE SOLUTION IN THE METASTABLE STATE, DELIVERING METASTABLE SUPERSATURATED SOLUTION TO THE CONTACT PORTION OF SAID LIQUID FLOW ZONE REMOVING CRYSTALLIZED SOLIDS FROM THE CONTACT PORTION OF SAID LIQUID FLOW ZONE, REMOVING SOLVENT SOLUTION SUBSTANTIALLY DEPLETED AS TO CRYSTALLIZABLE COMPONENT FROM A POINT REMOVED FROM SAID CONTACT PORTION OF THE LIQUID FLOW ZONE AND RECOVERING SOLVENT ASSOCIATED WITH THE REMOVED CRYSTAL SOLIDS AND THE NON-CRYSTALLIZABLE COMPONENT FROM THE RESPECTIVE PRODUCTS WITHDRAWN FROM THE SYSTEM. 